Process for hydrodesulfurization of cracked gas oils and the production of dimethyldecalins and fuel oil blending components



Dec. 2, 1969 M. c. KIRK. JR 3,481,996

PROCESS FOR HYDRODESULFURIZATION OF CRACKED GAS OILS AND THE PRODUCTION OF DIME'IHYLDECALINS AND FUEL OIL BLENDING COMPONENTS Filed Dec. 4. 1968 .2 Sheets-Sheet 1 4 Hz ID A 6 j/ S Distillation Hydro- I Sm er BR C4 400 F Tower 8R 400-675F Desulfurizer pp l I I2 Desulfurized I Gas Oil BR 400 F IO H2 x 8 2 H d BR C4'4OOF y I Stripper Desulfurlzer I S Distillation BR 40o F Tower l4 BR Desulfurized Gas Oil 5 BR 400 F*' FIG. 2

INVENTOR ATTORNEY M. c. KIRK, JR 3,481,996

ZATION OF CRACKED GAS OILS AND Dec. 2, i969 PROCESS FOR HYDRODESULFURI THE PRODUCTION OF DIME'IHYLDECALINS AND FUEL OIL BLENDING COMPONENTS 2 Sheets-Sheet 2 Filed Dec. 4, 1968 m w W U m 07- m K N C W T mm mm 79.96% mm m M m vm mm mm Ln 3 m mm m Y R @N at w 8 mm Ewu .5 N F w o 100$ mm? 5% :132 S m m comvsoov mm ..ovm-ow mm w m H S R N 53m 4 6 =mmo z m w B r6276 mm om m t :2 8 .0895? mm m .697 6 mm -Eu I 2 mm 1 m N S 2 N: m N; w mm 2 United States Patent O 3,481,996 PROCESS FOR HYDRODESULFURIZATION OF CRACKED GAS OILS AND THE PRODUC- TION OF DIMETHYLDECALINS AND FUEL OIL BLENDING COMPONENTS Merritt C. Kirk, Jr., Thornton, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Continuation-impart of application Ser. No. 532,298, Mar. 7, 1966. This application Dec. 4, 1968, Ser. No. 781,095

Int. Cl. C07c /10, 7/04 US. Cl. 260-667 12 Claims ABSTRACT OF THE DISCLOSURE Dimethyldecalins and fuel oil blending components having an improved cetane number and a decreased tendency to produce smoke on burning can be produced from cracked gas oil boiling mainly in the range of 400-675 F. by a process comprising (1) Separating from the cracked gas oil a lower boiling fraction, which fraction boils mainly below 550 F.,

(2) Hydrodesulfurizing the lower boiling fraction to produce a hydrodesulfurized product which contains less than 300 ppm. of sulfur,

(3) Separating from this hydrodesulfurized product a fraction boiling below about 480 F., a fraction boiling above about 540 F., and a fraction containing dimethylnaphthalenes and boiling mainly in the range of 480- 540 F.,

(4) Catalytically hydrogenating the 480 540 F. fraction to an aromatics content of less than 8% under hydrogenation conditions comprising a temperature in the range of 400-l000 F., a pressure in the range of 500-4000 p.s.i.g., a liquid hourly space velocity in the range of 0.1- 10.0 and in the presence of 5000-11000 s.c.f. of hydrogen per barrel of hydrocarbon feed, and

(5) Distilling the hydrogenated product of step (4) to recover a fraction containing at least 90% dimethyldecalins and boiling in the range of 400 450 F.

CROSS REFERENCES TO RELATED APPLICATIONS The present application is a continuation-in-part of Ser. No. 532,298, now Patent No. 3,424,673, issued Jan. 28, 1969, filed Mar. 7, 1966 of Merritt C. Kirk, Jr. entitled Process for Hydrodesulfurizing the Lower Boiling Fraction of a Cracked Gas Oil Blend, said application being copending with application, Ser. No. 225,034, filed Sept. 20, 1962 which matured into US. Patent No. 3,256,- 353 on June 14, 1966 in the name of Frank R. Shuman, Jr., and Merritt C. Kirk, Jr., and titled Preparation of Dimethylclecalins, all of these being assigned to Sun Oil Company. Certain catalysts and reaction conditions taught in copending application, Ser. No. 636,493, filed May 5, 1967, of Ivor W. Mills, Glenn R. Dimeler and Merritt C. Kirk, Jr., titled Process of Preparing an Aromatic Oil and Non-Discoloring Rubber Composition Containing Said Oil, which is also assigned to Sun Oil Company, are useful in practicing the present invention. Also useful in practice of one embodiment of the present invention is the disclosure of Patent No. 3,437,707 issued Apr. 8, 1969 which was copending application Ser. No. 627,887, filed Apr. 3, 1967 and assigned to Sun Oil Company of Merritt C. Kirk, Jr. and Craig R. Andersson, entitled Method of Treating Cracked Gas Oil, particularly the alkylation process and the process of recovering an aromatic concentrate of 2,6- and 2,7-dimethylnaphthalenes from cracked gas oil which are disclosed therein. The disclosure of all of these patents and applications is hereby incorporated in the present application.

SUMMARY OF THE INVENTION This invention relates to producing dimethyldecalins and fuel oils for fuel oil blending components having an improved cetane number and a decreased tendency to produce smoke on burning.

The dimethyldecalins are useful in the production of such dimethylnaphthalenes as 2,6-dimethylnaphthalene. The 2,6-dimethylnaphthalene can be oxidized to the corresponding dibasic acid which can be converted to a diester and the diester can be polymerized to produce a high molecular weight polyester which is useful in the production of fibers. The yield of 2,6-dimethylnaphthalene from a mixture of dimethyldecalins can frequently be improved by isomerization of the dimethyldecalins, such as is taught in US. Patent No. 3,243,469.

The present invention comprises (1) separating from a cracked gas oil boiling mainly in the range of 400- 675 F. a lower boiling fraction which is in the range of 40-70% of the total volume of the cracked gas oil and which contains, at least, most of the components of the gas oil which boil in the range of 400-550 F., (2) hydrodesulfurizing the lower boiling fraction to produce a hydrodesulfurized product which contains less than 300 ppm. of sulfur, (3) separating from this hydrodesulfurized product a fraction boiling below about 480 F., a fraction boiling above about 540 F., and a fraction containing dimethylnaphthalenes and boiling mainly in the range of 480540 F., (4) catalytically hydrogenating the 480-540 F. fraction to an aromatics content of less than 8% (more preferably less than 1%), (5) distilling the hydrogenated product of step (4) to recover a fraction containing at least dimethyldecalins and boiling in the range of 400-450 F.

Most preferably, the hydrodesulfurization of step (2) and the hydrogenation of step (4) are conducted under conditions such that the dimethyldecalin product of step (5) contains less than 20 and, more preferably, less than 5 p.p.m. of sulfur, when the dimethyldecalin product is to be used in the production of dimethyliaphthalenes, since the preferred nickle and noble metal-containing dehydrogenation catalysts are deactivated by sulfur-containing feeds. When the dimethyldecalin product is to be isomerized in the presence of a catalyst which is deactivated by aromatics (such as A1013), the hydrogenation of step (4) should be effected under conditions which, within the limits imposed by economics, reduce the aromatics content to the lowest attainable amount. Removal of residual aromatics (and polar heterocyclic compounds) prior to such an isomerization can be effected by means of adsorbents such as the alumino-silicate zeolites which are commonly referred to as molecular sieves (e.g., an acidictype Y zeolite) BACKGROUND OF THE INVENTION In the preparation of distillate fuel oil, such as household heating oils, cracked gas oils obtained from either catalytic or thermal cracking operations and boiling mainly in the range of 400-675 F. are generally used as components. In the United States, the refiner will frequently produce a desulfurized cracked gas oil which meets ASTM standards for No. 2 fuel oil and not market it directly as a heating oil but will blend it with other hydrocarbons, such as kerosene, and market the resulting blend as his brand of household heating oil. Such household heating oil blends normally contain a lower percentage of sulfur than does the desulfurized catalytic gas oil component, have more desirable ignition characteristics, a lighter color, and improved stability on storage. Occasionally, proprietary additives may be used to improve these properties of household fuel blends.

In such fuels as diesel oil and jet fuel, high aromaticity is detrimental because it raises the smoke number and decreases the cetane number.

For jet fuel or diesel fuel, requiring a high cetane number and low smoke number, conventional processing is from straight run (virgin) distillate fractions of crude oil since, unless the refiner invests in a solvent extraction plant to recover naphthalenes, there is no economical method of reducing the high aromatic content of crackedgas oils and, in particular, of catalytically cracked gas oils. Although severe hydrodesulfurization of abroad range cracked gas oil will cause hydrogenation of aromatics, thus raising the cetane number, such processing is usually too costly in view of the value of the improvement ob tained.

In the production of the lighter boiling distillate fuels, such as kerosene, diesel fuel, and jet engine fuel, it has been conventional to utilize a 300550 F. boiling range straight run naphtha fraction having a low sulfur content and low content of aromatic hydrocarbons. Such naphtha fractions are often desulfurized by sweetening processes (rather than by hydrodesulfurization) followed by clay contacting for color improvement.

The present invention is of particular advantage since, apart from obtaining high purity dimethylnaphthalenes as a valuable product, the less valuable products of the invention can be used by the refiner to more economically produce fuels having a lower aromatic hydrocarbon content that would normally be obtained from catalytic gas oil. In fact, the refiner is able by means of one embodiment of the present invention to utilize the highly aromatic 400-550 F. fraction, obtained by the distillation of catalytic gas oil, in such desirable fuels as diesel oil, kerosene, and even jet fuel.

In the preparation of dimethyldecalins, by the process of US. Patent No. 3,256,353, the feed stock to the hydrogenation stage, when using the usual catalysts containing noble metals, is a low sulfur content (under 20 parts per million, more preferably under 5 p.p.m., most preferably less than 1 p.p.m.) catalytic gas-oil fraction boiling between 480540 F. which is obtained from a 400-550 F. fraction of catalytic gas-oil. The nitrogen in such a feed stock should also be minimal (preferably less than 25 p.p.m., more preferably less than 5 p.p.m.). Usually, processes which reduce the sulfur to the desired level in a catalytic gas oil, will also reduce the nitrogen to the desired level. As is shown in US. Patent No. 3,256,353, such a 480540 F. feed stock can be obtained by distillation of an undesulfurized catalytic gas-oil fraction boiling between about 400-550 F., and then subjecting this 480-540 F. distillate to vapor phase hydrodesulfurization. However, in commercial operations, where the manufacture of dimethyldecalins is but one small part of an integrated refining scheme, such processing is usually not the most economical because the refiner has available a hydrodesulfurizer of a prefixed capacity (determined by the production of gas-oil boiling range material from his catalytic cracking operations) and it is not practical to utilize this hydrodesulfurizer to desulfurize only the 480540 F. material, which is but a small percentage of the total output of catalytic gas-oil.

Similarly, if the refiner obtains his 400--540 F. catalytic gas-oil fraction from a previously hydrodesulfurized, broad range catalytic gas oil boiling mainly in the range of 400675 F., he must hydrosulfurize this entire broad range catalytic gas-oil to less than 20 p.p.m. of sulfur in order to insure the desired low sulfur content in the 480-540 F. distillate obtained from a 400- 550 F. distillate fraction of the desulfurized broad range gas oil. Frequently, such a 480540 P. fraction obtained from a desulfurized broad range gas oil will actually have a higher sulfur content than the average sulfur content of the whole desulfurized broad range gas oil.

Normally, the refiner can recover some of the cost of desulfurizing the material boiling below about 550 F. which is not converted to dimethyldecalins, because the low sulfur content in these materials and the reduced aromatic content in the material boiling above about 450 F. (resulting from distillation of the hydrogenation product) make these materials highly desirable as blending components for jet fuel and diesel fuel. In periods of national emergency, any process which can increase the refinery yield of jet fuel may assume great importance.

It is more difficult to find uses for the gas-oil fraction boiling mainly above about 550 F. which will return to the refiner the added processing expense which he must incur in reducing the sulfur to about 20 p.p.m. (or, even, 300 p.p.m.). In addition, when the refiner attempts to use the higher boiling fractions of these low sulfur materials as fuel blending components he may find that they are less compatible with virgin gas-oil than similar fractions which were less severely desulfurized.

The above-mentioned disadvantages are avoided by practice of the process illustrated schematically in FIG- URE 3 whereby, for example, only the 400-5 50 F. fraction of the sulfur-containing catalytic gas-oil is hydrodesulfurized and the 550-675 F. fraction is not subjected to hydrosulfurization but is blended with low sulfur content fuel oil components, such as the 400-480 F. and the over 540 F. distillates recovered after removal of the 480-540 F. fraction of the 400-550 F. feed stock. The bottoms, boiling mainly above 450 F., obtained from distillation of the hydrogenation product of the 480-540 F. fraction are also useful as a blending stock.

If the refiner is concerned with maximizing his production of jet fuel, diesel fuel or #1 fuel-oil he can utilize these low sulfur-containing products of the 400- 550 F. desulfurized fraction as blending components, since they can be processed (if the cost of hydrogen is sufficiently low) to have a lower aromatic content and, thus, a higher cetane number and a lower smoke number than does the corresponding catalytic gas oil fraction. Normally, the refiner would not use the higher boiling material (such as the bottoms boiling above 450 F.) in jet fuel.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 of the attached drawings is a schematic flow sheet illustrating conventional plant scale practice for hydrodesulfurization of cracked gas oils to produce a partially desulfurized cracked gas oil to use as a major component of blended household fuel oil. In this conventional procedure, a whole gas-oil fraction boiling mainly in the range of 400675 F. is desulfurized.

FIGURE 2 of the attached drawings is illustrative of the procedure taught in the aforementioned copending application, Ser. No. 532,298. In this process, a catalytic gas-oil boiling mainly in the range of 400675 F. is separated, as by distillation, into a lower boiling fraction boiling mainly below about 550 F. and containing about 4080% of the total sulfur in the cracked gas oil and into a higher boiling fraction. Only the lower boiling fraction is hydrodesulfurized in the hydrodesulfurizer and the hydrodesulfurized product is blended with the higher boiling fraction to produce a blended product having a sulfur content no greater than the sulfur content would be if the entire cracked gas-oil was hydrodesulfurized in the hydrodesulfurizer at the same temperature and pressure conditions. For example, the catalytic gas oil is separated in distillation tower 2 into fractions boiling mainly in the range of 400-550 F. and 550-675 F. The 400-550 F. fraction is transported via line 13 to the hydrodesulfurizer 6. The hydrodesulfurized product is transported via line 8 to a stripper 9 wherein it is separated into an overhead fraction boiling below about 400 F. which is removed via line 11 and a bottoms product boiling above about 400 P. which is removed via line 12 and blended back with the undesulfurized 550675 F. distillate fraction in line 14 to produce a desulfurized gas oil which is transported via line 15.

FIGURE 3 illustrates the process of the present invention wherein the processing scheme of FIGURE 2 is practiced in conjunction with the preparation of dimethyldecaline is taught in the aforementioned U.S. Patent No. 3,256,353. One product of the present invention can be a blending component with an improved smoke number and improved cetane number due to removal from the fuel of dimethylnaphthalenes in the-480- 540" F. fraction of the cracked gas oil. In this procedure, the desulfurized product produced from, for example, a 400-550 F. fraction of catalytic gas oil is transported via line 8 to a stripper 9 where it is separated into a fraction boiling below 480 F. (as a 400480 F. fraction which can be transported via line 16), a fraction boiling above 540 F. (which can be transported via line 12), and a fraction containing dimethylnaphthalenes and boiling mainly in the range of 480-540 F. The 480 540 F. fraction can be transported via line 17 to a hydrogenator 18 wherein the 480-540 F. desulfurized catalytic gas oil is catalytically hydrogenated to an aromatics content of less than 8% (preferably less than 1%). The hydrogenation product is transported via line 20 to a splitter 21 wherein a fraction is separated containing at least 90% dimethyldecalin and boiling in the range of 400-450 F. The bottoms product from this distillation, boiling mainly above 450 F. can be transported via line 25 and, if desired, can be blended with various other fractions obtained in this process in order to produce desirable products such as jet fuel, diesel oil or household fuel. Alternatively, this bottoms product can be utilized as a cracking stock.

FURTHER DESCRIPTION OF THE INVENTION The 480-540 F. feed fraction can be catalytically hydrogenated to an aromatics content of less than 8% under hydrogenation conditions comprising a temperature in the range of 400l000 F., a pressure in the range of 50010,000 p.s.i.g., a liquid hourly space velocity in the range of 01-100 and in the presence of 5000 to 20,000 s.c.f. of hydrogen per barrel of hydrocarbon feed. The hydrogenated product can be distilled to separate a fraction containing at least 90% dimethyldecalin and boiling in the range of 400450 F.

All of the material in this 400550 F. fraction which is not recovered as dimethyldecalins can be combined with the desulfurized fraction boiling below 480 F. to produce an excellent fuel, meeting ASTM specification D 396-64T for #1 fuel, and which has a high cetane number and a low smoke number and is useful as a component of jet fuel and diesel fuel. This #1 fuel can also be blended with the stripper bottoms fraction boiling above 540 F. and with the undesulfurized higher boiling fraction of line 14 to produce a desulfurized gas-oil which is useful as a fuel or as a component of household heating oil.

The hydrodesulfurization step of the present invention can be effected at conditions including a temperature in the range of 5001000 F., a liquid hourly space velocity in the range of O.255, and a hydrogen rate of 2000- 10,000 s.c.f./bbl.

Although the invention of the aforementioned application, Ser. No. 432,298, can be practiced in connection with trickle phase hydrodesulfurization, utilizing processes such as those of U.S. Patent No. 2,608,521 or US Patent No. 2,897,141, the present invention is preferably practiced with vapor phase hydrodesulfurization since a more complete sulfur removal is required than can be economically obtained with trickle phase hydrodesulfurization. That is, in one preferred embodiment of the present invention, the hydrodesulfurized catalytic gas-oil fractions are further refined in processes utilizing nickel or noble metal catalyst (e.g., hydrogenation with platinum catalyst of dimethylnaphthalenes to dimethyldecalins) and, to prevent poisoning, the feed to such catalysts should contain less than about 50 parts per million of sulfur, preferably less than 20 p.p.m., more preferably less than 5 p.p.m., and most preferably less than 1 p.p.m.

Suitable catalysts for the hydrodesulfurization step and the hydrogenation step of the present invention include the solid sulfactive, oxide and/or sulfide-containing hydrogenation catalysts (e.g., sulfided nickel-molybdenum oxides) and the hydrogenation-dehydrogenation catalysts described in the aforementioned copending patent application, Ser. No. 638,493, filed May 5, 1967, by Ivor W. Mills, Glenn R. Dimeler and Merrit C. Kirk, Jr., entitled Process for Preparing an Aromatic Oil and Non-Dis- Coloring Rubber Composition Containing Said Oil. The process conditions taught in Ser. No. 638,493 as being applicable to the lower viscosity feeds (e.g., 40-65 SUS at 100 F.) are, in general, applicable in the hydrodesulfurization and hydrogenation steps of the present invention if the corresponding liquid hourly space velocity is increased by about 50%.

Other suitable catalysts and conditions for the hydrodesulfurization step of the present invention are those described in the aforementioned copending patent application, Ser. No. 532,298. When it is desired that hydrogen consumption be minimized in the hydrodesulfurization step of this process, the preferred catalysts are at least partially sulfided and comprise cobalt-molybdenum oxides, nickel-molybdenum oxides and nickel-cobalt-molybdenum oxides. Preferred conditions for such minimization of hydrogen consumption include a temperature in the range of 740-800 F., a pressure in the range of 350550 p.s.i.g., a hydrogen to oil ratio of 2:1 to 6:1, a hydrogen feed rate of 20004000 s.c.f./bbl. (with recycle) and a liquid hourly space velocity of 0.75-1.75.

Molecular sieve zeolites containing cobalt or nickel when composited with molybdenum oxide, such as the catalysts of U.S. Patent No. 3,098,032, can be used as catalysts for hydrodesulfurization of 400 5 50 F. cracked gas-oil fractions.

When the hydrogenation catalyst is sulfided nickelrnolybdenum oxides, the hydrodesulfurized catalytic gasoil fraction which is fed to the hydrogenation step of the present invention can contain as much as 0.5% of sulfur.

When utilizing a platinum-containing catalyst in hydrogenation of a dimethylnaphthalene-containing fraction, in order to produce dimethyldecalins according to the present invention, the 480-540 F. feed fraction should have a sulfur content no greater than about 300 ppm. (and With noble metal catalysts less than 20 p.p.m.) in order to prevent catalyst poisoning. Under conventional practice of producing compatible components for fuel blending, the entire catalytic gas-oil is hydrogenated to a sulfur content in the range of 0.1-0.5 percent. If this desulfurized gas-oil is distilled to obtain the 400-550 F. fraction from which a 480-540 F. dimethylnaphthalene feed fraction is to be obtained, this dimethylnaphthalene fraction will normally contain much more than 300 ppm.

of sulfur and would have to be subjected to additional desulfurization before hydrogenation. Normally, the refiner will produce such low sulfur content catalytic gas-oil fractions by vapor phase hydrodesulfurization in order to remove over of the sulfur in his feed.

Due to the influence of the catalytic cracking operations of a refinery in prefixing the capacity of the hydrodesulfurizer and the prefixing, in trickle phase hydrodesulfurization, of the maximum reaction temperature by the critical point of the feed stock, the refiner must either derive the feed for the dimethyldecalin process of U.S. Patent No. 3,256,353 from reformed heavy naphtha (which inherently contains little sulfur) or from cracked gas-oils which have been desulfurized in the gas phase, or in the liquid phase at pressures of 1000-10,000 p.s.i.g.

or he must subject the liquid phase, desulfurized cracked gas oil to an additional desulfurization step, such as a caustic wash followed by contact with an adsorbent.

In the preparation of dimethyldecalins from cracked gas-oil, vapor phase hydrodesulfurization of the 400- 550 F. fraction is preferred (particularly if noble metal containing catalysts are used in the hydrogenation Step). However, when the refiner does not have available a hydfrosulfurizer which may be operated in the vapor phase, he may use trickle phase hydrodesulfurization, to remove over 90% of the sulfur in a catalystic gas-oil fraction boiling mainly between 400550 F. and containing as much as 2% of sulfur (more preferably, less than 0.5% sulfur). In order to remove at least 90% of the sulfur in this catalytic gas oil fraction, in the trickle phase, he must hydrodesulfurize at about 725 F. and with at least 650 p.s.i.g. of hydrogen, at a liquid hourly space velocity of no more than 2 This removal will be at the expense of a greater hydrogen consumption, per pound of sulfur removed, than is incurred when utilizing trickle phase hydrosulfurization to remove only about 50% of the sulfur present in the gas oil. The severely, trickle-phase desulfurized product from the 400500 F. catalytic gas oil fraction can be further desulfurized to under 20 parts per million of sulfur (and, thus, be suitable for a noble-metal catalyzed hydrogenation step) by subjecting it to a wash in caustic soda followed by contact with a solid absorbent such as activated magnesium oxide using a process such as that disclosed in US. Patent No. 3,121,678. Acid extraction, as with 3-30 wt. percent of anhydrous HF at 30-120 F. can also be used to reduce the sulfur to below 20 p.p.m. but is usually too expensive.

The 480540 F. gas oil fraction which is hydrogenated in the production of dimethyldecalin, can contain in the order of 300 parts per million of sulfur if the hydrogenation catalyst comprises sul-fided nickel-molybdenum oxides or platinum supported on eta-alumina, such as the catalysts disclosed in US. Patent No. 2,965,564.

EXAMPLE A catalytic gas oil fraction, containing about 0.5% sulfur and boiling mainly in the range of 400-550 F., is obtained by distillation (as that in the process scheme of FIGURE 2) of a catalytic gas oil boiling mainly in the range of 400-675 F. This 400-550 F. fraction is processed according to the schematic diagram of FIG- URE 3. The 400550 F. fraction passes along line 13 and enters the hydrodesulfurizer 6. Hydrogen enters the hydrodesulfurizer through line 7 and is recycled (via lines which are not shown). The hydrodesulfurization is effected in vapor phase, as at 775 F. and 450 p.s.i.g. with hydrogen recycle of about 5000 s.c.f. at a liquid hoursly space velocity of 1.2. The catalyst is sulfided cohalt-molybdenum oxides on an alumina support.

The hydrodesulfurized product, containing less than 10 ppm. of sulfur, is transported through line 8 to the stripper 9, where dry gas (H 8, NH and hydrocarbons containing less than 4 carbon atoms) is distilled and removed via line 10, and where the remainder of the product is separated by distillation into a gasoline fraction boiling mainly below 400 P. (which is removed via line 11), a 400-480 F. fraction (which is removed via line 16), a bottoms fraction boiling above 540 F. (which is removed via line 12) and a 480-540 F. boiling range fraction, containing less than 10 p.p.m. of sulfur, which is transported via line 17 to the hydrogenator 18. Hydrogen enters the hydrogenator via line 19 and is recycled (via lines which are not shown).

Hydorgenation is effected over a platinum-on-etaalumina hydrogenation catalyst at a temperature of 650 F., a pressure of 1200 p.s.i.g., a hydrogen rate of 8000 s.c.f. per barrel and a liquid hourly space velocity of 0.75 volumes of oil per volume of catalyst per hour. This 480-540 F. feed has an aromatics content of 50%, a

saturate content of 50 and a dimethylnaphthalene content of 22%. The hydrogenated product of this 480-- 540 F. feed fraction, which has an aromatics content of 0.5% and a dimethyldecalin content of 20%, is transported via line 20 to a splitter 21, where it is separated by distillation into a dry gas fraction (which is removed via line 22), a gasoline fraction (which is removed via line 23), a bottoms fraction boiling mainly above 450 F. (which is removed via line 25) and a fraction having an initial boiling point of 400 F. and an end boiling point of 450 F. (which is removed via line 24). This 400-450 F. fraction analyzes dimethyldecalins, the remaining 10% being essentially saturated hydrocarbons.

The remaining portions of the desulfurized product of the 400 550 F. gas oil fraction are transported, through lines 16, 12 and 25 to collection points 30, 28 and 26, respectively. The 400480 F. boiling range material collected at point 30 can be further transported to point 32 via line 31 where it can be blended by means of a mixing valve with the remainder of the original catalytic gas-oil boiling mainly between 550-675 F. or, alternately, it can be transported to point 28 where it can be blended with the bottoms fraction from the stripper, boiling mainly above 540 F., and/0r blended with the bottoms fraction from the splitter, boiling mainly above 450 F., which is transported from collection point 26 to collection point 28 via line 27. Any of these fuel components or fuel component blends can be removed for further blending or can be transported via line 28 to point 33 where they can be blended with the remainder of the catalytic gas-oil, boiling mainly above 550 F., in order to produce a blended fuel.

The percentage 2,7- and 2,6-dimethyldecalin in the 400-450 F. product from the splitter 21 can be greatly increased by alkylating the desulfurized 480540 F. fraction with an alkyl aromatic, or an alkyl halide or an olefinic hydrocarbon (as by adding an alkylation reactor 17a and distillation column 17b to line 17) and removing the alkylation products boiling above about 540 F. by distillation. The so-removed alkylation products are useful as plasticizers for polyvinyl chloride. One preferred alkylation reagent is light stable (olefinic) gasoline since this reagent does not require the use of pressure vessels. Another advantage of using this reagent is that the recovered gasoline will have a reduced olefin content, which is of aid in reducing air pollution. Other preferred olefinic reagents are the C -C acyclic monoolefins (e.g., propylene, butene-l, isobutylene) and mixtures thereof. The molecular sieve zeolite catalysts are one class of preferred catalyst (e.g., see US. Patent No. 3,121,754, US. Patent No. 3,140,253 and P. B. Venuto et al., Alkylation Reactions Catalyzed by Crystalline Aluminosilicates, ACS Preprints, September 1965 ACS Meeting, pages B-71 to B-88).

The dicyclic aromatic content of the 480--540 F. fraction can also be increased by solvent extraction of aromatics, as before such an alkylation reaction, or before the hydrogenation step. Means of concentrating the aromatics in this fraction, by solvent extraction (as with furfural), are described in the aforementioned copending application of Merritt C. Kirk, Jr., and Craig R. Andersson, Ser. No. 627,887 now Pat. No. 3,424,673 issued Jan. 28, 1969 (which also discloses useful conditions for the alkylation reaction) and in US. Patent No. 3,172,919 to Hagerty et al.

The invention claimed is:

1. Process of producing dimethyldecalins from cracked gas oil boiling mainly in the range of 400675 F., said process comprising (1) separating from said cracked gas oil a lower boiling fraction which is in the range of 4070% of the total volume of said cracked gas oil and which contains, at least, most of the components of said cracked gas oil which boil in the range of 400- 550 F., (2) hydrodesulfurizing said lower boiling frac- 9 tion to produce a hydrosulfurized product which contains less than 300 ppm. of sulfur, (3) separating from said hydrodesulfurized product of step (2) material boiling below about 480 F., a fraction boiling above about 540 F and a fraction containing dimethylnaphthalenes and boiling mainly in the range of 480-540 F., (4) catalytically hydrogenating said 480-540 F. fraction to an aromatics content of less than 8%, distilling the hydrogenated product of step (4) to recover a fraction containing at least 90% dimethyldecalins and boiling in the range of 400-450 F. and a fraction boiling mainly above 450 F.

2. Process according to claim 1 wherein in said step (4) the hydrogenation conditions comprise a temperature in the range of 400-1000 F., a pressure in the range of SOD-10,000 p.s.i.g., a liquid hourly space velocity in the range of 0.110.0 and the presence of 5000-20,000 s.c.f. of hydrogen per barrel of hydrocarbon feed.

3. Process according to claim 1 wherein said hydrodesulfurized product of step (2) contains less than 20 p.p.m. of sulfur and wherein step (4) is efiected by means of a catalyst comprising at least one metal selected from the group consisting of nickel, platinum, palladium, rhenium and rhodium.

4. Process according to claim 1 wherein said hydrodesulfurization of step (2) is effected in the presence of a sulfided catalyst comprising cobalt-molybdenum oxides, nickel-molybdenum oxides or nickel-cobalt-molybdenum oxides.

5. Process according to claim 4 wherein said hydrosulfurization of step (2) is effected at conditions including a temperature in the range of 5001000 F., a liquid hourly space velocity in the range of 0.25-5, and a hydrogen rate of 2000l0,000 s.c.f./bbl.

' 6. Process according to claim 5 wherein said conditions of step (2) include a temperature in the range of 740-800 F., a pressure in the range of 350-550 p.s.i.g., a hydrogen to oil ratio of 2:1 to 6:1, a hydrogen feed rate of 2000-7000 s.c.f./bbl. and a liquid hourly space velocity of 0.75-1.75.

7. Process according to claim 1 wherein in step (3) a fraction boiling mainly in the range of 400-480 F. is separated and wherein said 400-480 F. fraction is combined with said fraction boiling above about 450 F. of step (5), to produce a fuel meeting ASTM specification D396-64T for #1 fuel said fuel having a high cetane number and a low smoke number and being useful as a component of jet fuel and diesel fuel.

8. Process according to claim 7 wherein at least some of said fraction boiling mainly above 450 F. of step (5) is blended with the higher boiling fraction produced in step (1) and with the fraction boiling above about 540 F. of step (3) to produce a desulfurized gas oil which is useful as a motor fuel or as a component of household heating oil.

9. Process according to claim 1 wherein said lower boiling fraction of step (1) boils mainly in the range of 400-550 F. and wherein in step (3) there is separated from said hydrodesulfurized product of step (2) a fraction boiling mainly in the range of 400 480 F.

10. Process according to claim 1 wherein said dimethyldecalin product contains less than 1% aromatic compounds and is catalytically isomerized to increase its content of 2,6-dimethyldecalin.

11. Process according to claim 10 wherein said isomerized dimethyldecalin mixture is further processed to recover 2,6-dimethylnaphthalene.

12. Process according to claim 1 wherein said fraction of step (3) which contains dimethylnaphthalenes and boils mainly in the range of 480-540 F. is

(a) alkylated with an alkylation reactant comprising a C -C hydrocarbon or a monochlorinated C -C hydrocarbon,

(b) the alkylated fraction from step (a) is distilled to recover a fraction boiling substantially within the range of 480-540 F. and a higher boiling fraction which is useful as a plasticizer, and

i (c) said 480-540 P. fraction of step (b) is catalytically hydrogenated in said step (4).

References Cited UNITED STATES PATENTS 3,256,353 6/1966 Shuman et a1 260667 3,243,469 3/1966 Schneider 260668 3,349,139 10/1967 Jafii'e 260667 DELBERT E. GANTZ, Primary Examiner V. O. KEEFE, Assistant Examiner U.S. Cl. X.R. 

